When Light Just Isn’t Fast Enough

Take a speed of light trip across the solar system starting at the Sun

We’ve heard it over and over. There’s nothing faster than the speed of light. Einstein set the speed limit at 186,000 miles per second (299,792 km/sec). No material object can theoretically travel faster. For all practical purposes, only light is lithe enough to travel at the speed of light.

Moving in such haste, a beam of light can zip around the Earth 8 times in just one second. A trip to the moon takes just 1.3 seconds. Fast for sure but unfortunately not fast enough. Hit play on the video and you’ll soon know what I mean. The view begins at the Sun and travels outward into the solar system at the speed of light.

Planet           Distance in AU            Travel time
Mercury              0.387        193.0 seconds   or    3.2 minutes
Venus                0.723        360.0 seconds   or    6.0 minutes
Earth                1.000        499.0 seconds   or    8.3 minutes
Mars                 1.523        759.9 seconds   or   12.6 minutes
Jupiter              5.203       2595.0 seconds   or   43.2 minutes
Saturn               9.538       4759.0 seconds   or   79.3 minutes
Uranus              19.819       9575.0 seconds   or  159.6 minutes
Neptune             30.058      14998.0 seconds   or    4.1 hours
Pluto               39.44       19680.0 seconds   or    5.5 hours

Distances and light times to the planets and Pluto (from Alphonse Swinehart)

You might first think that moving that fast will get us across the orbits of the eight planets in a hurry. I shouldn’t have been surprised, but I found myself already getting impatient by the time Mercury flew by … after 3.2 minutes. Earth was still 5 minutes away and Jupiter another 40! That’s why the video cuts off at Jupiter – no one would stick around for Pluto’s appearance 5 1/2 hours later.

As the video tediously but effectively demonstrates we live in a solar system where a few planets are separated by vast spaces. Not even light is fast enough to satisfy the human need for speed. But just to put things in perspective, the fastest current human-made objects is NASA’s Voyager I spacecraft, which recently reached interstellar space traveling at 38,000 mph (17 km/sec) or nearly 18,000 times slower than light speed.

Let’s explore further. Any material object, a Skittle for instance, moving that fast would become infinitely massive. Why? You’d need an infinite amount of energy to accelerate the Skittle to the exact speed of light. Since matter and energy are two faces of the same coin, all that energy creates an infinitely massive Skittle. Sweet revenge if there ever was.

You can however accelerate the pill-like candy to 99.9999% light speed with a finite if incredibly large amount of energy. Einstein’s cool with that. Here’s the weird thing. If you were travelling along at the speed of light it would look like a perfectly normal piece of candy, but if you were to look at it from the outside world, the sugary treat would be the entire universe. Both viewpoints are equally valid, and that’s the essence of relatively.

Wave-particle duality of light

To better imagine a day in the life of a photon, let’s go along for the ride. Photons are the particle form of light, which for a long time was only understood as waves of electromagnetic energy. In the weirdness of quantum world, light is both a particle and a wave. From our perspective, a photon rip by at 186,000 miles per second, but to the photon itself, the world stands still and time stops. Photons are everywhere at once. Omnipresent. No time passes for them.

In relativity theory, the movement of anything is defined entirely from an observer’s point of view. From the photon’s perspective, it’s at rest. From ours, it’s moving across time and space. We all have our own “coordinate frame”, so that wherever we are, we’re at rest. That’s relativity for you – all frames are equally valid.

Let say you’re in a plane. That sad bag of pretzels you were just handed is at rest because it’s in your coordinate frame. The person next to you is likewise at rest (and hopefully not snoring). Even the plane’s at rest. According to Einstein, it’s just as valid to picture the world outside the airplane window moving while the plane itself remains at rest. Next time you fly, close your eyes once the plane reaches altitude and a constant speed. You’ll hear the noise of engines, but there’s no way to know you’re actually moving.

Diagram showing how an object (sphere) contracts in the direction of motion as its speed increases. At far left, its velocity (V) is 0.3 times the speed of light. Credit: Askamathematician.com
Diagram showing how an object (sphere) contracts in the direction of motion as its speed increases. At far left, its velocity (V) is 0.3 times the speed of light. Credit: Askamathematician.com

Relativity also predicts that objects contract in the direction of their motion. Strange as it sounds, this has been verified by many experiments. The faster things travel, the more they contract.

The effect doesn’t become noticeable until an object approaches light speed, but the Apollo 10 service and crew modules reached a velocity of 0.0037% the speed of light. From the perspective of someone on the ground, the 11.03-meter-long module shrank by approximately 7.5 nanometers, an exceedingly tiny but measurable amount. (A sheet of paper is 100,000 nanometers thick). Likewise, distances contract, bottoming out at zero at light speed.

Length contraction occurs because a stationary observer sees a speedy spaceship traveler’s time tick by more slowly. Since light is measured in time units – light seconds, light years – in order for the two to agree on the speed of light (a constant across the universe) the traveler’s “ruler” has to be shorter. And it really is from your stationary perspective if you could somehow peer inside the ship. Traveling at 10% light speed, a 200-foot spaceship shrinks to 199 feet. At 86.5%, it’s 100 feet or half the size and at 99.99% only 3 feet!

We’ve traveled far today – sitting quietly in our frames of reference.

35 Replies to “When Light Just Isn’t Fast Enough”

  1. Thank you Bob yet another great article, Just to put things into perspective light from the Sun hits Earth in 8.3 minutes and hits Pluto in 330 minutes that gives us a better way of realising the vast distances even within our own Solar System…:)

    1. If I had a picture of Clint Eastwood painted on the side of a car that could reach the speed of light. The picture would be distorted to observers standing still, but the picture if I looked out the window would look like Clint Eastwood, seeing that I would be traveling the same speed.

      The reality is that the perception has changed based on the observers perspective. But, the picture (unless dissolved via the energy necessary to reach such speed) will in reality continue to be a picture of Clint Eastwood.

      This is the whole problem with physicist and scientist in other fields attempting to assume that they have expertise in philosophy or questions concerning of the nature of reality. The ship doesn’t expand or change size, only the perception “An Optical illusion” of the observer changes. The equipment used to measure sates of particle/waves are distorted because they as are our eyes not capable of detecting exact positions. But to say that reality changes based on ones perception is hogwash!

      There are deterministic and realistic interpretations of quantum mechanics that is seldom discussed in the main stream media. It seems only strange or extravagant interpretations gets much press or consideration. There is no reason to believe that just because our eyes or equipment cannot capture the exact position in the quantum world, that such a position does not exist.

      It is assumed that time as defined by mechanical clocks is the only perspective of time that exist. But time “That which keeps everything from happening at once” is quite different than ones perception, or a mechanical clocks effects under various conditions.

      Like the picture of Clint Eastwood, simultaneity is real despite ones perception or perspective, or inability to capture it mechanically. Just because a camera would not be fast enough or powerful enough to capture the image of Clint Eastwood on a car moving at the speed of light, nor can observers or machines capture the exact position of sub some atomic particles or photons. But that does not mean that they are moving and standing still or that they can be in two or more positions at once, it simply means we do not have the means to capture it with our own perspective or with modern technology.

      Sorry Bob, but you really should include other interpretations and perspectives and stop assuming that there is only one interpretation of the evidence. Your position is based totally on a false perception of the true nature of reality.

      1. One thing is sure; that is one badass car- travelling light speed with a Clint Eastwood paintjob.

      2. Krydan,
        You’re right. It’s all perception or frames of reference. But time dilation and mass increase with speed has all been measured with great precision. The Twins Paradox for instance is true. I think it’s important to take relativity’s lesson to heart that there is no absolute “correct” perspective. Clint Eastwood’s picture really is changing as the car approaches light speed – at least as experience in our world.

      3. It changes how? If you mean that the molecules will break down and the paint will dissolve; yes! But the image is a hypothetical question as is a spaceship traveling light speed would rip to shreds as in your analogy,

        The point I was getting at is that just because our eyes or our most advanced recording systems “cameras” cannot correctly capture an images true nature at high speeds, does not follow logically that the nature of the image has changed, Only your perception of that reality is distorted by the motion of the image: even at much lower speeds within the realm of possibilities you’d get this same effect.

        The image in my analogy would remain an image of Clint Eastwood at the speed of sound, despite you not being able to identify its true nature standing still.

        If you are saying that at light speed that the image would change; how would it change?

        Again, If you are then shifting to the effects that the rate of speed would have on the paint aka the molecules breaking down and dissolving; then you obviously cannot grasp the difference seeing that the ship you imagine too would dissolve under such a condition.

        We are talking hypothetically “if” a “ship” or if ” A painting on a car” If the car stopped and the picture was still in tact; then explain to us what it the picture was approaching the speed of light? Then what about your ship? Do the objects physically and in reality change or transform into another entity based on your perception? There certainly is no evidence that I am aware of that things changed physically, unless you mean being torn asunder under the forces of nature when coming in contact with a speck of dust.

      4. During an edit of a sentence I accidentally cut out a section leaving the question unrecognizable.

        The question was: Approaching light speed what does the picture become? And for that matter what does the ship become? We can only speculate, because we do not have the technology to test in the macro-world such experiences, It is assumed that in the quantum world that weird crazy things are happening, appearing in what “Appears” to be two places at once. But there are interpretations of quantum mechanics that does not make such assumption; but, rather interprets it as being simply our inability to accurately measure or understand these observations: In other words, this so called strange world of quantum mechanics is not really so strange, our perception is!

        And our perception is based on our faulty receptors, and mechanical devises that cannot accurately capture what is going on.

        I am looking at this from a philosophical point of view: Science is as good as our perception; if our perception or philosophical assumptions are not based on the true nature of reality, you will get all kinds of wacky and strange interpretations.

        I just think the mainstream media gives a lot of credence to one side of this issue: There are 10 different interpretations of what the evidence means; yet is seems only wacky or strange opinions make the front page. Just curious as to why we should assume that the macro world is strange just because we do not fully understand what we are seeing in the quantum world?

        To jump to conclusions macro world, based on our faulty perceptions of the minute seems backwards to me.

      5. To answer you question, the image of Clint does NOT change. What does change, is the space itself. Any given length of space gets reduced a certain amount. This is what reduces wave length of objects approaching us, and creates the “red shift” of objects receding away from us. The shapes of objects “change” because the space containing the objects shrinks or gets elongated, depending on whether it is approaching to or receding from the observer.

      6. Tihomir

        Again, this would be an optical illusion when talking about solid objects, they would break apart if elongated beyond their breaking point. A baseball thrown at 100 mph may have an appearance of being elongated, but that would be an illusion. If the ball was actually travelling at a speed wherein its actual shape changed it would eventually rip apart at some point, long before reaching anything close to the speed of light.

        You can speed up a film till it looks like people and objects are leaving trails, or are elongated. But that is merely an optical illusion! In the quantum world things are occurring that simply cannot be captured by our eyes or fastest frame rate recorders. This does not mean that things are in reality in two places at once etc…. These are assumptions based on one interpretation. There are 10 different interpretation of quantum mechanics, and deterministic models that does not require that we accept these more wacky ideas about the nature of reality. Stephen Hawking is right about one thing when he talks about “Model Dependent Realism” We really do build models based on our perceptions of reality. We could perceive that the picture of Clint Eastwood actually changes, or simply accept that it is a simple optical illusion.

        Something appearing or being relevant to the observer only applies to the illusion, In Einsteins famous observers on a train, as opposed to those witnessing the same event standing still can be best explained as: The light will appear to reach the target at different points to the various observers, but there is an actual point wherein the light actually reaches the target. To suggest that the light reaches its target at various times based on its observers sounds wacky, because frankly it is: There is simultaneity despite our inability to grasp it from our various perspectives. These experiences has sounded like silly musing of an wannabe philosopher that should have be satisfied with just being a great physicist.

  2. so the wavelength of a photon if slowed down to “normal” speed would be in the infra red / radiowave spectrum??

    1. Zoutsteen,
      Light speed changes by varying amounts depending upon the medium in which it travels. For instance, when it travels from air into glass or water its speed changes slightly at the interface, as does its wavelength and hence color.

      1. What is significant is that the speed of light, in those varying mediums, only slows down. Nothing yet has provided evidence that it can be sped up relative to it’s defined, normative speed.

  3. Makes you wonder how much the New Horizon’s vehicle contracted. And what is the time difference it has achieved during it’s flight.

    1. I can’t remember if it was New Horizon or one of the Voyager probes, but I read an article that actually provided that calculation. It was on the order of less than a second or two as I recall, but I could be recalling it incorrectly too.

  4. I’ve always wondered about one thing. If the mass of an object increases exponentially as it is pushed closer and closer to light speed, why wouldn’t it eventually form a black hole? I know it might seem that an object would have to be pushed all the way to light speed to do this, but stars that collapse on themselves to form black holes just have a lot of mass, not an infinite amount.

    1. It makes you wonder if black holes are a result of an object approaching lightspeed relative to some other object. Picture the following scenario, two stars in different parts of the universe or even the same galaxy get caught in some form of a gravity slingshot at around the same time but in opposite directions and both approach at least half the speed of light. Now since they are relatively traveling away from each other wouldn’t both technically achieve lightspeed and/or become black holes?

    1. rrsquez,
      True, but my point was that Einstein determined the speed of light to be the universal speed light. No object can move faster. Space is different and can expand at many times the speed of light.

  5. Thank you Bob. One practical side of this is that with the billion of dollars spent annually on cosmetics and miracle diets, we could fund every space programs by demonstrating that from other people’s point of view, contributors’ looks will be lasting a lot longer and their waist line will contract. Where’s Dr Oz when we need him?

      1. That’s a cool answer list, Bob! My favorite answer there is labeled “answer 6” and it’s my favorite since it is simple and complete enough to answer the question.

  6. To be specific, General Relativity only says that nothing can REACH the speed of light. It does not prohibit the existence of particles that already travel beyond that speed (thus, not requiring acceleration).

  7. Space is expanding, correct? So if light leaves a star 10b ly away, than it will take longer than 10 billion years to reach us?

    So at some point space will expand faster than the speed of light. Won’t we be moving faster than the speed of light?

    Sorry for posting two questions.

    1. wreckhur,
      You can post as many questions as you like. The more the merrier. Yes,
      space is expanding, so yes, the light will take longer than 10 billion years to get here due to the expansion of space during the time the light has traveled.
      Space expanded faster than the speed of light back during cosmic inflation and in the current era at edge of our visible horizon. What’s expanding faster than the speed of light is spacetime itself. Think of galaxies as raisins in a loaf of bread cooking in the oven. The dough represents spacetime. As the dough expands, the raisins move apart even though they’re not moving relative to spacetime. They’re just going along for the ride.
      Another way to look at it is to imagine you’re in a galaxy at the cosmic horizon looking back in the direction of the Milky Way. From your perspective you measure our galaxy’s velocity to be nearly the speed of light. That’s because there’s so much expanding spacetime between us, we appear to be traveling at near light speed. From even farther away, the Milky Way would appear to move faster than the speed of light. But here at home, we’re not affected by cosmic expansion but by gravitational attractions within the Local Group of galaxies and the Local Supercluster, yielding much lower velocities.
      I hope this helps at least a little to answer your excellent question.

  8. Thanks Bob for additional information…
    In the reference you provided, “Answer 6” says :
    “Matter is usually defined as something that has both a rest mass and a volume. Photons have neither of these so they are not considered matter. When something is moving very fast, close to the speed of light, it starts to gain extra mass because of relativity. This is why photons, which move at the speed of light, have mass…” (!)
    As I understand, we need to stay around as long as possible, to learn what the “light” (photon) is…!
    If scientists discover the “dark matter” and explain what it is, we (or some others) may learn the “true story” of the light (photon)…

    1. “This is why photons, which move at the speed of light, have mass…” (!)”

      Actually that is why photons CAN move the speed of light at all… They have no mass at all, so that “no mass”, when closing in on the speed of light multiplies into… more and more NO MASS. If they and the others of the particle zoo with no mass HAD mass, they would not be (thus are not) able to travel that fast. ANY initial mass ends up becoming, for the particles that DO have it, SO large when closing in on that speed, it becomes infinite which in turn makes an infinite amount of energy be needed to move them TO that actual speed. Hence the impossibility of surpassing this exquisite physical barrier. 😉

  9. A nice video, even if somewhat boring at times (and thus proving the point of the vastness of space :-).
    The funny thing is, if we were moving along with the photon travelling at the speed of light, like in the movie, there’d be no “time passed” and “time left to the next planet” counters, they’d both be zero. For anything moving at the speed of light, just as you mentioned, time stands still. No time passes for a photon emitted at the first light of the CMB, which hits a detector on the Earth now, some 13 billion years later. So, for the photon in the movie, it reaches all the objects alongs its path at the same “time”: the moment it leaves the Sun. Relativistically speaking, the time counters refer to the time observed by a viewer sitting on Earth (or the Sun actually) and watching the photon travel away.
    Another nitpick: once you pass an object and continue travelling away from the Sun, you don’t get to see much of the object lit by the Sun as in the video (look at Jupiter for the bect effect), since the Sun would be illuminating the side pointing away from you.
    Still a great video though 🙂 – thanks for sharing it!

  10. I find nothing wrong in what you say, Bob, but I think you do not say enough to explain any of the phenomena you mention. You start out with the speed of light and you do a good job of that (just like most textbooks do), then you go on to make some amazing claims from Special Relativity and “contractions,” then about the dual nature of light, a little about time, and finally sum it up with it all being based on the observer’s perspective. It’s all well and good, IMO.
    And yet, you give us no idea about how all that is part of the same universe, how it is “the theory of everything” (TOE) if only we could simply connect all the dots.
    Well, I have some ideas on how to do just that. I began with trying to figure out what time is, and determined it is a property of discrete matter and passes inversely proportional to the speed of any given object. How fast anything ages depends on its speed through the universe.
    Next, I thought about the concept of entropy, and that made me think that time is the fifth fundamental force that causes matter to age.
    From the Twin Paradox and another riddle I call the Train Paradox, which is more easily understood, I learned about time dilation and understood it to be not dilation of time or space, as Einstein thought, nor created out of the observer’s perspective, but that it is a property of the universe.
    The rate of the passage of time for matter is based on its speed, so objects moving at different speeds will have different time rates, whether or not anyone is around to see them. Time “dilations” occur all the time (pun) as a natural process. Observers do not create them when they observe matter from different reference frames; it is not their perspective that does it, it is their speed differences. The proof is that two observers moving at a constant speed with respect to each other will age at the same rate even if they are galaxies apart.
    One caveat: No observer can ever have the same perspective as another observer when their speed is not the same. None can ever see or know another observer’s time rate from frames of different speeds. Yet, we can be sure the others’ time rate is the same if their speeds are the same.
    I have solved the riddle of light duality and posted my theory in U. Today in another topic. I welcome your thoughts, good or not.

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